Holocene Temperature Variations in Semi-Arid Central Mongolia—A Chronological and Sedimentological Perspective From a 7400-year Lake Sediment Record From the Khangai Mountains

Abstract

Semi-arid Mongolia is a highly sensitive region to climate changes, but the region’s Holocene paleoclimatic evolution and its underlying forcing mechanisms have been the subject of much recent debate. Here we present a continuous 7.4 ka sediment record from the high-altitude Shireet Naiman Nuur (Nuur = lake) in the central Mongolian Khangai Mountains. We extensively dated the sediments and analyzed elemental composition and bulk isotopes for lake sediment characterization. Our results show that 14C-dating of bulk organic carbon and terrestrial macrofossils provide a robust and precise chronology for the past 7.4 ± 0.3 cal ka BP at Shireet Naiman Nuur and 14C-ages are mostly in stratigraphic order. The 14C-based chronology is confirmed by paleomagnetic secular variations, which resemble the predictions of spherical harmonic geomagnetic field models. The very good chronological control makes paleomagnetic secular variation stratigraphy a powerful tool for evaluating and refining regional 14C-chronologies when compared to the record presented here. The lake sediment proxies TOC, N, log (Ca/Ti) and log (Si/Ti) reveal increased lake primary productivity and high growing season temperatures from 7.4 ± 0.3 to 4.3 ± 0.2 cal ka BP, which is likely the result of stronger summer insolation and pronounced warming. Reduced summer insolation thereafter results in decreased productivity and low growing season temperatures at Shireet Naiman Nuur from 4.3 ± 0.3 cal ka BP until present day. The globally acknowledged 4.2 ka event also appears as a pronounced cooling event at Shireet Naiman Nuur, and additional abrupt cooling events occurred during minima in total solar irradiance at ∼3.4, 2.8 and 2.4 ka BP. Low lake primary productivity and growing season temperatures are likely the result of longer ice cover periods at the high-altitude (2,429 m a.s.l.) Shireet Naiman Nuur. This leads to shorter mixing periods of the lake water which is supported by more positive δ13CTOC because of increased incorporation of dissolved HCO3− by aquatic producers during periods of longer ice cover.

Increasing Spring Insolation in the Late Holocene Intensified Aeolian Activity in Dryland Asia

“…Comparing the aeolian intensity with the reconstructed westerlies index (Z. S. An et al, 2012), the Siberian High intensity (Mayewski et al, 1997) and the percentage of hematite-stained grains from the North Atlantic (Bond et al, 2001), our result shows that intense aeolian activity in western Mongolia corresponded to ice-rafting events (Events 0, 1, and 2; Figure 3f) in the North Atlantic, strong westerlies (Figure 3d), and the Siberian High (Figure 3e) during the late Holocene. The multiproxy records from Shireet Naiman Nuur in semiarid central Mongolia suggest a cooling climate during the late Holocene (Bliedtner et al, 2022), consistent with the result of pollen-based paleotemperature reconstruction for the North European mainland (Seppä et al, 2009) (Figure 3g). The Siberian High and the westerlies can be significantly strengthened by cooling at high latitudes, resulting in more frequent penetrations of cold air masses from high latitudes and more intense aeolian activity in downwind areas.…”

“…Based on meteorological data and empirical orthogonal function analysis, it was demonstrated that snow cover had a positive relationship with wind velocity related to Asian dust events in the spring months (Kurosaki & Mikami, 2004; Ryu et al., 2018). Compared with the Gobi Desert in southern Mongolia, the warming rate in the Altai Mountains area is low because of more glacial advance events and/or ice‐cover periods on millennial timescales during the late Holocene (Agatova et al., 2012; Bliedtner et al., 2022; Herren et al., 2013; J. D. Zhao et al., 2013), possibly leading to higher temperature gradients and stronger surface winds in spring, such as the 2021 mega dust event in Mongolia (Figure S7 in Supporting Information ). It was also claimed, based on meteorological data and modeling, that an increase in the frequency of dust days in the East Asian dust source regions was due to an increase in the frequency of strong winds (Kok et al., 2021; Kurosaki & Mikami, 2003).…”

Assessing Lock-in Depth and Establishing a Late Holocene Paleomagnetic Secular Variation Record From the Mongolian Altai

“…For the semi-arid regions of Mongolia, we recently proposed a dual chronological approach in the high-altitude Shireet Naiman Nuur (Nuur = lake) sediments (46°31'55.04"N, 101°49'16.23"E; Khangai Mountains, central Mongolia), where we (1) established a high-resolution 14 C-chronology for the past 7.4 cal. ka BP by dating terrestrial macrofossils and (2) corroborated the 14 C-based chronology by a newly obtained PSV record from the lake (Bliedtner et al 2022). The PSV record from Shireet Naiman Nuur very well confirms our 14 C-based chronology and provides a valuable regional master record for using PSV stratigraphy in semi-arid Mongolia to evaluate and potentially refine 14 C-chronologies when compared to our record.…”

“…BP [95.4%]). However, no hardwater effect was presently indicated by modern 14 C-ages of the modern water plant (Strobel et al 2021;Bliedtner et al 2022). Based on the 14 C-ages, a chronology was established for the Khar Nuur sediments by Bayesian age-depth modeling using the Bacon 2.3.4 package in R (Blaauw and Christen 2011).…”

“…In this context, paleomagnetic secular variation (PSV) stratigraphy is a valuable chronostratigraphic tool to evaluate and potentially refine 14 C-based chronologies (Barletta et al 2010;Ólafsd óttir et al 2013;Haberzettl et al 2015Haberzettl et al , 2019Haberzettl et al , 2021Bliedtner et al 2022). PSV changes are ideally suited to study shortterm changes especially throughout the Holocene.…”